1. Field of the Invention
The present invention relates to creped sanitary tissues which are extremely soft, absorbent and drapeable making them especially suitable for such products as bathroom tissue, facial tissue and napkins.
2. Description of Background Art
In the manufacture of sanitary tissue, a significant challenge to the papermaker is to make tissues which are not only soft, absorbent and thick but also strong. Typically, softness, absorbency, and thickness are inversely related to strength. Several avenues are available to the papermaker for improving product quality. For example, to improve sheet absorbency and thickness, one can use a thru air dried process as disclosed in U.S. Pat. No. 3,301,746 by Sanford and Sisson or one can incorporate bulking fibers into the web as disclosed in U.S. Pat. No. 3,434,918 by Bernardin, U.S. Pat. No. 4,204,504 by Lesas et al., U.S. Pat. No. 4,431,481 by Drach et al., U.S. Pat. No. 3,819,470 by Shaw et al., and U.S. Pat. No. 5,087,324 by Awofeso et al. Bulking fibers can take the form of mechanical pulp or other thermally/chemically cross-linked fiber. Thicker more absorbent structures can be made using a low batting papermaking felt as described in U.S. Pat. No. 4,533,457 by Curran et al.
To improve tissue softness, several approaches are available to the papermaker such as using certain species of hardwood like eucalyptus in stratified webs as discussed in U.S. Pat. No. 4,300,981 by Carstens and U.S. Pat. No. 3,994,771 by Morgan et al. U.S. Pat. No. 3,821,068 by Shaw discloses a technique for producing a soft tissue structure by avoiding mechanical compression until the sheet has been dried to at least 80% solids. U.S. Pat. No. 3,812,000 by Salvucci et al. discloses a technique for producing a soft tissue structure by avoiding mechanical compression of an elastomer containing fiber furnish until the consistency of the web is at least 80% solids. U.S. Pat. No. 3,301,746 by Sanford and Sisson discloses a thru air dried papermaking technology for producing soft tissue structures. U.S. Pat. No. 5,164,045 by Awofeso et al. discloses a technique for making a soft tissue product by combining foam forming, stratification, and bulking fibers. Finally, U.S. Pat. No. 4,063,995 by Grossman discloses advanced creping technologies for improving the softness of tissue products.
Numerous references suggest the broad use of a myriad of alternative fibers for making generic "paper". High strength specialty papers have been made using non-woody fibers (usually termed "hard" or "cordage" fibers) such as sisal, abaca, hemp, flax and kenaf. As described in McLaughlin and Schuck, Econ. Bot 45 (4), pp 480-486, 1991; such fibers are commonly used for such products as currency paper, bank notes, tea bags, rope paper, filters, air cleaners and other products requiring "scruff" and tear resistance along with high endurance for folding. McLaughlin and Schuck suggested that such specialty products can also be formed from fibers derived from the genera Hesperaloe and Yucca in the family Agavaceae and that "their long, narrow fibers may be superior to other species currently used for pulping." Surprisingly, in light of the literature described and discussed above suggesting that these hard or cordage fibers be used for specialty papers requiring high strength and scruff resistance, we have found that chemically pulped fibers derived from the leaves of the genus Hesperaloe in the family Agavaceae are especially suitable for making extremely high quality creped tissue paper having outstanding softness and drapeability coupled with extremely high strength. McLaughlin and Schuck report neither fiber coarseness for the fibers under considerations nor the strength of papers made from these fibers making predictions about suitability for tissue-making at least very problematic, if not impossible. Accordingly, the present invention is directed to a creped tissue paper product having extremely high strength along with outstanding bulk, absorbency and softness wherein at least about 20% by weight of the fiber is derived by chemical pulping from leaves of the genus Hesperaloe, preferably Hesperaloe funifera. Preferably, the sanitary tissue paper product may consist essentially of at least about 40% Hesperaloe funifera fibers, the remainder being a fiber blend chosen from the group consisting of softwoods, hardwoods, anfractuous (bulking) fibers and recycled fiber.